JPS62119722A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To form the titled magnetic recording medium having excellent still image durability and S/N by incorporating a binder contg. a sulfo group and/or a phospho group as the alkali metal salts and >=2 kinds of nonmagnetic particles having different particle diameter distribution into a magnetic layer. CONSTITUTION:The binder contg. a sulfo group and/or a phospho group as the alkali metal salts and >=2 kinds of nonmagnetic particles having >=5 Mohs' hardness and having different particle diameter distribution from each other are incorporated into the magnetic layer. The mean particle diameter of the first kind of nonmagnetic particles is adjusted to <=0.5mum, the mean particle diameter of the second kind of nonmagnetic particles is controlled to >0.5mum, and the first kind of nonmagnetic particles is incorporated, by a weight ratio, more abundantly than the second kind of nonmagnetic particles. When this binder is used, the dispersibility of magnetic powder is improved, the surface smoothness of the magnetic layer is ameliorated, and the contamination of a calender roll, etc., is reduced. Furthermore, the S/N and the dropout as well as the still durability can be sufficiently improved by this magnetic layer.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to magnetic recording media such as magnetic tapes and magnetic sheets.

BACKGROUND ART In recent years, magnetic recording media, especially video magnetic recording media that require short wavelength recording, have become smaller and finer than ever before.
There is a growing tendency to use magnetic powder with high magnetic force. However, as magnetic powder becomes finer and has higher magnetic force,
The cohesive force of individual particles becomes stronger, and as a result, the dispersibility and surface smoothness required for obtaining high reproduction output and good S/N ratio for short wavelength recording are no longer fully satisfied. In addition, since such recording media come into intense sliding contact with the magnetic head during recording and reproduction, repeated use causes the magnetic coating to wear out, and the magnetic powder contained in the coating is likely to fall off, causing undesirable problems such as clogging of the magnetic head. produce results.

For this reason, it is possible to improve the dispersibility of the magnetic powder in the binder by adjusting the particle size distribution of the magnetic powder, to use a surfactant as a dispersant, or to improve the dispersibility of the magnetic powder in the binder. Methods have been proposed in which the properties are modified by introducing a phospho group, a sulfo group, a carboxy group, or the like.

For example, by introducing a sulfonic acid metal salt residue into a polyester resin,
JP-A-74827, etc. disclose improvements in surface smoothness (gloss) and adhesion to supports; JP-A-56-13519; JP-A-56-74826;
No. 74829, etc. discloses improvements in fillability related to dispersibility and interfacial tension, and the binder composition is improved by combining the sulfonic acid metal base-introduced polyester resin, polyurethane resin, nitrocellulose, vinyl chloride-vinyl acetate resin, etc. Many proposals have been made.

Furthermore, since vinyl chloride resin has high mechanical strength, vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride copolymer, vinyl chloride-acrylonitrile copolymer, or vinyl chloride-vinyl acetate-vinyl alcohol- Maleic anhydride copolymers and the like are preferred.

Modification of the vinyl chloride resin with a sulfonic acid metal salt residue is disclosed in JP-A-57-44227, and first, a vinyl chloride resin containing an OH group and, for example, 1
A dehydrochloric acid reaction is carried out between a compound containing a chlorine atom and a sulfonic acid metal salt residue in the molecule to obtain a modified vinyl chloride resin having a sulfonic acid metal salt residue introduced therein.

A vinyl chloride copolymer containing a free sulfo group (-3O3H) is disclosed in JP-A-58-108032.

However, when a vinyl chloride copolymer obtained from such a polymerizable monomer having a free sulfo group is mixed with a magnetic paint, the dispersibility of the magnetic powder may be excellent in the dispersion process. However, a rapid increase in viscosity occurs within a short period of time after dispersion and before coating, and even if coating is possible, an undesirable medium is often obtained. In addition, the calender rolls are often contaminated during the calendering process after coating, and as a result, there is a significant difference in performance between the media obtained by initial coating and the media obtained after coating, and most media are unsatisfactory. It only showed the appropriate S/N and output.

Therefore, as mentioned above, by using as a binder a polymer in which a metal salt of a polymerizable unsaturated sulfonic acid is copolymerized with vinyl chloride, the above drawbacks can be considerably improved. However, on the other hand, when such a binder is used, there have been cases where the durability has been reduced (in particular, the output has been reduced when used for a long period of time).

An object of the present invention is to provide a magnetic recording medium that has excellent dispersibility of magnetic powder and good durability, particularly excellent still image durability, and excellent S/N ratio. .

22 Structure of the invention and its effects, that is, the present invention provides a magnetic recording medium having a magnetic layer containing a magnetic powder binder. The magnetic layer contains a binder (made of at least a vinyl chloride resin) and two or more types of non-magnetic particles having a Mohs hardness of 5 or more and having different particle size distributions, and the non-magnetic particles The average particle size of the first type of non-magnetic particles is 0.5
μm or less, and the average particle size of the second type of non-magnetic particles exceeds 0.5 μm, and the first type of non-magnetic particles are larger than the second type of non-magnetic particles in terms of weight ratio. The present invention relates to a magnetic recording medium characterized by containing:

According to the present invention, since the binder contains a sulfo group and/or a phospho group in the form of an alkali metal salt, the dispersibility of the magnetic powder is improved and the surface smoothness of the magnetic layer is improved. Less dirt on calendar rolls, etc. Moreover, since the magnetic layer contains two or more types of non-magnetic particles with a Mohs hardness of 5 or more in the particle size distribution and ratio described above, durability during long-term use, which is the problem with the binder described above, is improved. It is possible to prevent the deterioration in performance and to perform control so as to exhibit sufficient performance not only in still durability but also in terms of S/N ratio and dropout.

In the present invention, the term "two or more types of nonmagnetic particles" refers to different types of nonmagnetic particles, even if they have different compositions, or even if they are the same but have different physical properties. It is also possible to simply have a different particle size distribution.

In the present invention, the first of the non-magnetic particles (abrasives) used is
The average particle size of these types is 0.5 μm or less (preferably 0.5 μm or less).
．． 1 μm or more), and the other type has an average particle size of 0
．． Since the particle size is greater than 5 μm (preferably 0.8 μm or less), the particle size of the nonmagnetic particles can be well controlled. In the latter type of particles, it is a preferred embodiment that particles having a particle size of 1 μm or more account for 5 to 30% by weight. In addition, the ratio of rain particles is set to a weight ratio of second non-magnetic particles/first non-magnetic particles that is less than 1.0, so that it is possible to sufficiently prevent a decrease in output and obtain a high S/N. However, the blending ratio a is preferably set to 0.01≦a<1.0. If this ratio a is less than 0.01, the durability tends to decrease, and if it is 1.0 or more, the S/N will be significantly lowered.

Here, the above-mentioned "average particle size" may be measured by directly selectively counting with an electron microscope, or may be measured from particle size distribution using a laser beam or the like. It can also be calculated as a sphere from the specific surface area. Other known methods can also be used. For details, see rcARBON B
See LACK Yearbook 1984J (Carbon Black Association line), "Carbon Black Handbook" (Carbon Black Association line), and "New Experimental Chemistry Course Volume 18" (Japan Chemical Society line, 1978, published by Maruzen Co., Ltd.), etc. can.

The particle size of the non-magnetic powder with a Mohs hardness of 5 or more used in this magnetic medium can be known from surface photographs and tomographic photographs.

Nonmagnetic particles with a Mohs hardness of 5 or more that can be used in the present invention include alumina (preferably α-A 1203 ), silicon carbide, chromium oxide, silicon nitride, titanium oxide, α-
There are iron oxides, etc., but there are no restrictions on the types of inorganic or organic particles (and alloys may also be used. The content of these nonmagnetic particles is preferably 20% by weight or less based on the magnetic powder.

The binder according to the present invention, especially the vinyl chloride copolymer, is a copolymer containing vinyl chloride monomer, an alkali salt of sulfonic acid or phosphoric acid (raw monomer and other copolymer monomers as necessary). This copolymer can be obtained by copolymerizing.Since this copolymer is based on vinyl synthesis, it is easy to synthesize, and various copolymerization components can be selected, making it possible to optimally adjust the properties of the copolymer. I can do it.

The metal of the salt of sulfonic acid or phosphoric acid is an alkali metal (
In particular, sodium, potassium, lithium) are preferred, and potassium is particularly preferred in terms of solubility, reactivity, yield, and the like.

The above-mentioned copolymerizable monomer containing a sulfonate salt is CH2=CH3O3M.

CH2=CHCH2So　3　M.

CH2=C(C)(3)CH2S03M.

CH2=CHCH20COCH (CHz CC00R)
-3O3゜CH2CH2020CH2CH(OH)CHz-3O3
M.

CH2=C(CH3)COOC2H4SO3M.

CHz=CHCOOC+He SO3M.

CH2=CHC0NHC(CH3)2CH2SO3M is mentioned.

In addition, as a phosphate, CHz=CHCHzOCRzCH(OH)CH2-2-
0-P03', CH2=CHC0NHC(CHa)2CH2CH2-C
HCH20(CH2CH20)m-PO2MX2 In the above, M is an alkali metal and P has 1 to 2 carbon atoms.
0 alkyl groups, Yl is H, M or CH2=CHC0
NHC)I2CH(OH)CH2-1(CH2CHz
O) Ding, OH or OM, X2 is CH2=CHCH20(
CH2CH20) Ding, OH or OM. Also, n is 1
~100, m is a positive number from 1 to 100.

Copolymerizable polymers to be copolymerized as necessary include known polymerizable monomers, such as various vinyl esters, vinylidene chloride, acrylic acid, grillic acid, methacrylic acid, various acrylic esters, and medacrylic esters. , ethylene, propylene, isobutyne, butadiene, isoprene, vinyl ether, aryl ether,
Examples include polyester, acrylamide, methacrylamide, maleic acid, and areic acid ester.

The binder according to the present invention is polymerized by a polymerization method such as emulsion polymerization, solution polymerization, suspension polymerization, or bulk polymerization.

In either method, known techniques such as divisional addition or continuous addition of molecular weight regulators, polymerization initiators, and monomers can be applied as necessary.

The amount of the acidic group salt-containing monomer in the binder used in the present invention is preferably 0.01 to 30 mol%. If the amount of the salt-containing monomer is too large, the solubility in solvents is poor and gelation is likely to occur. Moreover, if the amount of salt-containing upper salt is too small, desired properties cannot be obtained.

In particular, the vinyl chloride copolymer as the binder is preferably used in combination with a urethane resin that improves the durability of the magnetic medium.

Furthermore, various conventionally known resins may be used in combination. The thermoplastic resin used in combination has a softening temperature of 150°C or lower, an average molecular weight of about 1000 to 200000, and a degree of polymerization of about 200 to 2000, such as vinyl chloride-vinyl acetate copolymer, vinyl chloride-vinylidene chloride, etc. Copolymer, vinyl chloride-acrylonitrile copolymer, acrylic ester-acrylonitrile copolymer, acrylic ester-vinylidene chloride copolymer, alkrylic ester-styrene copolymer, methacrylic ester-acrylonitrile copolymer, methacryl Acid ester vinylidene chloride copolymer, methacrylic acid ester-styrene copolymer, polyvinyl fluoride, vinylidene chloride-acrylonitrile copolymer, butadiene-acrylonitrile copolymer,
Polyamide resin, polyvinyl butyral, cellulose derivatives (cellulose acetate butyrate, cellulose diacetate, cellulose triacetate, cellulose propionate, nitrocellulose, etc.), styrene butadiene copolymer, polyester resin, chlorovinyl ether acrylate copolymer, Amino resins, various synthetic rubber-based thermoplastic resins, mixtures thereof, and the like are used.

Furthermore, the thermosetting resin or reactive resin has a molecular weight of about 200,000 or less in the state of a coating solution, and the molecular weight becomes infinitely large due to reactions such as condensation and addition. Furthermore,
Among these resins, those that do not soften or melt before the resin is thermally decomposed are preferred. Specifically, for example, phenol resin, epoxy resin, urea resin, melamine resin, alkyd resin, silicone resin, acrylic reaction resin, mixture of high molecular weight polyester resin and isocyanate prepolymer, methacrylate copolymer and diisocyanate prepolymer. Examples include mixtures, mixtures of polyester polyols and polyisocyanates, urea formaldehyde resins, mixtures of low molecular weight glycols/high molecular weight diols/triphenylmethane triisocyanates, polyamine resins, and mixtures thereof.

The resins mentioned above are -303M and -0503M.

It may be a resin containing a hydrophilic polar group such as -COOM, -PO(OM') 2 (where M is hydrogen or an alkali metal, and M' is a hydrogen, alkali metal, or hydrocarbon residue).

The blending ratio of the vinyl chloride copolymer and urethane resin that can be used in the present invention (the total of both is 100 parts by weight) is 90 to 1
It is desirable that the amount is 0 parts by weight, more preferably 80 to 20 parts by weight. If the above-mentioned blending ratio exceeds 90 parts by weight, the coating film becomes too brittle and the durability of the coating film is significantly deteriorated, and the adhesion to the support also deteriorates. Further, if the above-mentioned blending ratio is less than 10 parts by weight, the magnetic powder tends to fall off.

Furthermore, durability can be improved by further adding a polyisocyanate curing agent to the magnetic paint containing the binder according to the present invention. Such polyisocyanate curing agents include, for example, bifunctional isocyanates such as tolylene diisocyanate, diphenylmethane diisocyanate, and hexane diisocyanate, and trifunctional isocyanates such as Coronat (manufactured by Nippon Polyurethane Industries, Ltd.) and Desmod Shikaku Bayer Co., Ltd. or urethane prepolymers containing isocyanate groups at both ends, which have been conventionally used as curing agents, and any polyisocyanate that can be used as a curing agent can be used. The polyisocyanate curing agent is used in an amount of 5 to 80 parts by weight based on the total amount of binder.

FIG. 1 shows a magnetic recording medium, for example a magnetic tape, according to the present invention, which includes a support 1, a subbing layer 2 (this layer may not be provided if necessary), and a magnetic layer 3.
are laminated.

Based on the present invention, the above-mentioned binder, nonmagnetic abrasive particles, and magnetic powder are contained in the magnetic layer 3.

The support 1 is preferably coated with a so-called backcoat 4 as shown in FIG. 2 on the side opposite to the side on which the magnetic layer is provided for purposes such as antistatic and transfer prevention.

The magnetic powder used in the magnetic layer, especially the ferromagnetic powder, is 1
-Fe 203, CO containing r F13203, Fe3
O4, CO-containing iron oxide magnetic powder such as Fe3O4: Fe
SN is Co, Fe-N1-Go gold alloy Fe
-Mn-Zr3 alloy, Fe-Ni-Zn alloy, Fe-G
o-Ni-Cr alloy, Fe-Co-N1-P alloy, Go
-Ni alloy etc., Fes Nis C.

Metal magnetic powder mainly composed of: Various ferromagnetic powders such as Croz can be mentioned.

In addition to the above, additives such as a dispersant, a lubricant, and an antistatic agent may be added to the magnetic layer.

Other dispersants that can be used in combination include those having 8 to 22 carbon atoms, such as caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, oleic acid, elaidic acid, linoleic acid, lylunic acid, and behenic acid. Fatty acids (RIC
ool, R1 has 7 to 21 carbon atoms (alkyl or alkenyl group of II); the alkali metal of the fatty acid (Li,
Nas K, etc.) or alkaline earth metals (M g s C
a s B a ) metal soap; fluorine-containing compound of the above fatty acid ester; amide of the above fatty acid; lecithin; trialkyl polyolefin oxy quaternary ammonium salt (alkyl has 1 to 5 carbon atoms, olefin has ethylene) , propylene, etc.) are used.

In addition to these, higher alcohols having 12 or more carbon atoms and sulfuric esters may also be used.

These dispersants are added together with the phosphoric acid ester according to the present invention in an amount of 0.5 to 20 parts by weight based on 100 parts by weight of the magnetic powder.

As a lubricant, dialkyl polysiloxane (alkyl has 1 to 5 carbon atoms), C0OR (R=H or C1 to C
Dialkylpolysiloxanes modified with 2o alkyl groups), dialkoxypolysiloxanes (alkoxy has 1 to 4 carbon atoms ([11)], monoalkylmonoalkoxypolysiloxanes (alkyl groups have 1 to 5 carbon atoms, alkoxy has 1 carbon atoms) ~4 pieces,) silicone oil such as phenylpolysiloxane, fluoroalkylpolysiloxane (alkyl has 1 to 5 carbon atoms); conductive fine powder such as graphite; inorganic fine powder such as molybdenum disulfide and tungsten disulfide; polyethylene , polypropylene, polyethylene vinyl chloride copolymer, polytetrafluoroethylene, and other plastic fine powders; α-olefin polymers; unsaturated aliphatic hydrocarbons that are liquid at room temperature (n-olefin double bonds bonded to the terminal carbon Compounds (approximately 20 carbon atoms); fatty acid esters consisting of fatty acids with 12 to 22 carbon atoms and monohydric alcohols with 1 to 20 carbon atoms, fluorocarbons, etc. can be used. It is added in an amount of 0.2 to 30 parts by weight.

Antistatic agents include conductive fine powder such as carbon black and carbon black graft polymer; natural surfactants such as saponin; nonionic surfactants such as alkylene oxide, glycerin, and glycidol; higher alkylamines, and Cationic surfactants such as quaternary ammonium salts, pyridine and other heterocycles, and phosphoniums; Anionic surfactants containing acidic groups such as carboxylic acid, sulfonic acid, phosphoric acid, sulfuric acid ester groups, and phosphoric acid ester groups; Amino acids Amphoteric activators such as aminosulfonic acids, sulfuric acid or phosphoric acid esters of amino alcohols, etc. are used. The amount of the above conductive fine powder is 0.2 to 20 parts by weight per 100 parts by weight of the magnetic powder, and the amount of surfactant is 0.2 to 20 parts by weight.
It is added in an amount of 1 to 10 parts by weight. These surfactants may be added alone or in combination. Although these are used as antistatic agents, they are sometimes applied for other purposes, such as dispersion, improving magnetic properties, improving lubricity, and as coating aids.

In addition, the following may be used as additives. Phosphoric acid, sulfamide, guanidine, pyridine, amines, urea, zinc chromate, calcium chromate, strontium chromate, etc. can be used, especially dicyclohexylamine nitrite, cyclohexylamine chromate, diisopropylamine nitrite, jetanolamine phosphate, cyclohexyl ammonium carbonate. , hexamethylene diamine carbonate, propylene diamine stearate, guanidine carbonate, triethanolamine nitrite, morpholine stearate, etc. (inorganic acid salts or organic acid salts of amines, amides, or imides) improve the rust prevention effect. These are 0.01 to 2 parts by weight per 100 parts by weight of ferromagnetic fine powder.
It is used in a range of 0 parts by weight.

In addition, the constituent materials of the magnetic layer are mixed with an organic solvent to prepare a magnetic paint, which is coated on a support.
) alcohols (e.g. methanol, ethanol, propatool, butanol), esters (e.g. methyl acetate, ethyl acetate, butyl acetate, ethyl lactate, glycol acetate monoethyl ether)
, glycol ethers (eg, ethylene glycol monoethyl ether, ethylene glycol diethyl ether, dioxane), aromatic hydrocarbons (eg, benzene, toluene, xylene), aliphatic hydrocarbons (eg, hexane, heptane), nitropropane, and the like. The support to which this magnetic paint is coated can be polyester (e.g. polyethylene terephthalate, polyethylene-2,6-naphthalate), polyolefin (e.g. polyethylene, polypropylene), cellulose derivative (e.g. cellulose triacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate). propionate), polycarbonate, polyvinyl chloride, polyimide, polyamide, polyhydrazides, metals (eg aluminum, copper), paper, etc.

E, Example Hereinafter, the present invention will be explained with reference to specific examples.

The components, proportions, order of operations, etc. shown below may be changed in various ways without departing from the spirit of the invention.

In addition, in the following examples, all "parts" represent "parts by weight."

In the following examples, vinyl chloride copolymers containing the above salts were synthesized as follows.

The following composition was charged into a reaction vessel, replaced with N2, and reacted.

Methyl isobutyl ketone 86 parts by weight Methyl acetate 280 Vinyl chloride
150 Vinyl acetate
50〃H2 =CHCHzOCOCH, (SO3K)CH2COOC
eHpr 6" diisopropyl peroxydicarbonate (polymerization initiator) 2 The above formulation was raised to 53°C while stirring, and 9 parts of methyl isobutyl ketone was added to 1 part of the polymerization initiator in the recipe. After 15 hours, the temperature was raised to 30°C. The remaining vinyl chloride was recovered by cooling to a temperature of 32% and the remaining vinyl chloride was further recovered under reduced pressure.In this way, the solid content was 32% and the viscosity was 7.
480 parts by weight of a copolymer solution at 0 cps (25°C) was obtained.

Next, the formulation consisting of the ingredients shown in Table 1 was charged into a ball mill and dispersed. After filtering this magnetic paint through a 1 μm filter, 5 parts of polyfunctional isocyanate was added, and the mixture was coated on a support to a thickness of 5 μm. and put on a super calendar, 2
Video tapes (corresponding to the numbers of each Example and Comparative Example) were prepared by slitting the tape into inch width pieces. However, the numbers after the second column of Table-1 represent parts by weight, and "actual" after the second column represents an example, and "ratio" represents a comparative example. In Example 4, a back coat layer containing carbon black was provided.

(The following margins continue on the next page.) The same procedure as in the above synthesis example was carried out, except that CH3 Akebono CHz=CH-CONH-C-CH2-3O3HCH3 was used as the polymerizable unsaturated sulfonic acid as ratio-4. A videotape was made in the same manner as in Ratio-1 using the vinyl chloride resin synthesized.

Table 2 shows the performance of each example videotape.

(The following is a margin, continued on the next page.) However, regarding chroma S/N and RF output, actual -1,2
, 3 are relative values when the ratio -1 is set to O.

Real-4 is a relative value when ratio-2 is set to 0.

From this result, if a magnetic layer is formed based on the present invention,
It can be seen that magnetic powder has excellent dispersibility, improves the durability of the medium, and therefore has excellent magnetic and electrical properties.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, and FIGS. 1 and 2 are enlarged sectional views of a portion of the second side of the magnetic tape. In addition, in the symbols shown in the drawings, 1......Nonmagnetic support 2......Subbing layer 3...Magnetic layer 4. ...... Back coat layer.

Claims (1)

[Claims] 1. A magnetic recording medium having a magnetic layer containing magnetic powder and a binder, in which the binder contains a sulfo group and/or a phosphor group in the form of an alkali metal salt and a Mohs hardness of 5.
The magnetic layer contains two or more types of non-magnetic particles having different particle size distributions, and the average particle size of the first type of non-magnetic particles among the non-magnetic particles is 0.5 μm.
or less, and the average particle size of the second type of nonmagnetic particles is 0.
A magnetic recording medium characterized in that the first type of non-magnetic particles exceeds 5 μm and the first type of non-magnetic particles are contained in a weight ratio larger than the second type of non-magnetic particles.